# Why connect capacitors to motor body?

So I've found a motor circuit which looks like this:

Since many users here believe that my hand-drawn circuit schematics are in fact pictures of flying spaghetti monster, I'll also provide a written description:

There are two input lines marked + and - going to the motor. There is a capacitor connected in parallel with the motor. There is one capacitor connected to the positive side of the motor and the motor's metallic body and there is one capacitor connected to the negative side of the motor and the motor's metallic body. The capacitors look like multilayer ceramic capacitors and have capacitance of $0.1 \mbox{ } \mu F$. The motor is a Kysan Electronics FK-180SH-3240 DC motor. It is also worth noting that the motors have nominal voltage of 3 V, but are powered by a 2 cell LiPo battery and are controlled by a microcontroller-based circuit.

So my question is: Why use 3 capacitors, with two being connected to the motor body? It would seem logical to have capacitors on motor terminals to keep interference away from the microcontroller, but I don't see how having capacitors soldered to the motor body would help.

• It's good to see a fellow Pastafarian in our midsts... – Majenko Sep 15 '11 at 11:25
• I came across something identical to your post while I was repairing one of my Remote Controlled cars. According to what I found out on the internet is that the main purpose of the capacitors is to reduce noise produced by the DC motor, that can affect nearby appliances. There are 3 ways of connecting the capacitors. Here is a link of the detailed methods: beam-wiki.org/wiki/Reducing_Motor_Noise – user56769 Oct 23 '14 at 17:44